1. Field of The Invention
The invention relates to aromatic carbonate polymers of controlled molecular weight and more particularly relates to such polymers end-capped with a class of aromatic carboxylic acids or equivalent acid chlorides.
2. Brief Description of the Prior Art
It is known that in certain procedures of producing aromatic carbonate polymers from dihydric phenols and a carbonate precursor such as phosgene small amounts of certain weight regulators or chain terminators can be used to provide end or terminal groups on the carbonate polymer and thereby control the molecular weight of the polycarbonate. Such materials include phenol and p-tertiary-butylphenol.
The prior art also disclosed several other types of compounds that act as chain terminators for the carbonate polymers. Thus, U.S. Pat. No. 3,085,992 discloses alkanol amines as chain terminators; U.S. Pat. No. 3,399,172 teaches imides as chain terminators; U.S. Pat. No. 3,275,601 discloses that aniline and methyl aniline function as chain terminators in the interfacial polymerization process for producing polycarbonates; and U.S. Pat. No. 4,001,184 discloses primary and secondary amines as molecular weight regulators for polycarbonate. Furthermore, U.S. Pat. No. 3,028,365 discloses that aromatic amines and other monofunctional compounds can be used to control or regulate the molecular weight of the polycarbonates, thereby forming aryl carbonate terminal groups. Aromatic polycarbonates having carbonate end groups are disclosed in U.S. Pat. No. 4,111,910. These polycarbonates are prepared using a terminating amount of ammonia, ammonium compounds, primary cycloalkyl, aliphatic or aralkyl amines and secondary cycloaklkyl, alkyl or aralkyl amines.
However, according to Schnell, Chemistry and Physics of Polycarbonates (1964), page 183, ammonium hydroxide and amines saponify polycarbonates back to the monomers, i.e., bisphenol A. This is supported by Bolgiano in U.S. Pat. No. 3,223,678 wherein he indicates that small amounts of amines such as monoethanolamine and morpholine break or degrade polycarbonates into lower molecular weight polycarbonates. Thus, this area of chemistry is generally not very well understood and is one where the empirical approach is still generally the method used to determine whether a particular compound or class of compounds will function as effective chain terminators or terminal groups in polycarbonate. This area is yet further complicated by the fact that, even though a particular compound may be a chain terminator, its presence as a terminal group in the polycarbonate polymer may adversely affect the physical properties of the polycarbonate or molding compositions of polycarbonates.
A more recent improvement in the prior art is represented by the use of aroyl halides to terminate polycarbonate resin chains; see U.S. Pat. 4,448,953 to Rosenquist, et al. However, many other improvements are sought over prior art methods for polycarbonate chain termination. For example, the use of phenols as chain terminators in the preparation of polycarbonates leads to the formation of significant levels of the corresponding diaryl carbonates as contaminants. Because of the volatility of these diaryl carbonates, they "plate out" during thermal processing onto the molds and processing equipment, i.e.; they condense on the surfaces of the molds, the processing equipment and also onto the surface of the molded article itself.
We have now found that the use of certain carboxylic acids and acid chlorides as terminators in the preparation of polycarbonates affords resins with lower plate-out. The use of these low plate-out resins will reduce molding down time, thus affording higher productivity of a given resin processing line.
In addition, mixtures of various carboxylic acids can be used to fine tune the properties of the resin. For example, stearic acid may be used with benzoyl chloride to afford a low plate-out resin with improved release properties. Other advantages of the invention will be described below.